Adding custom events in the dashboard's task stream

I’d like to add a simple vertical line to indicate the occurrence of a certain event in the task stream dashboard. Is there a way I could patch in some code to achieve that?

Example:

As a secondary question, the thread How to use the Dask Discourse gives the example “How to create a new dashboard panel for a custom workflow” as thread topic, but I have unfortunately found no such thread nor page in the dask docs. Did I miss it?